In a projection-type image display device that displays a display screen of an image display element on a projection surface in an enlarged manner, its illumination optical system has been devised so as to obtain an enlarged image with sufficient size and brightness on the projection surface. In particular, a projection-type image display device using solid light-emitting elements, such as red, green and blue light-emitting diodes, organic ELs or the like, has been developed.
For example, a light source device that emits excitation light emitted from a solid light source as visible light with high efficiency has been proposed (see Patent Document 1).